test: make subr mocks variadic for native-comp, add arity meta-test

Re-enabling native-comp surfaced a suite-wide fragility. When a test redefines a C primitive (or a native-compiled function), native-comp routes native callers through a trampoline that calls the mock with the primitive's maximum arity. A fixed-arity mock narrower than the primitive then throws wrong-number-of-arguments, intermittently, as the eln-cache fills.

I swept every arity-narrow subr mock to append &rest _ (188 sites, preserving any named args the body uses), and added tests/test-meta-subr-mock-arity.el, which fails make test on any subr mock too narrow for the primitive's arity. The rule isn't "never mock a subr". The suite mocks message and completing-read freely. It's "a subr mock must accept the primitive's arity."

Background, the three failure modes, and the research are in docs/native-comp-subr-mocking.org.

1 files changed, 3 insertions, 3 deletions

diff --git a/tests/test-org-webclipper-commands.el b/tests/test-org-webclipper-commands.el
index be7fc38cf..fb693192f 100644
--- a/tests/test-org-webclipper-commands.el
+++ b/tests/test-org-webclipper-commands.el
@@ -120,7 +120,7 @@ that registers the webclip entry.  Providing `'org-protocol' fires the block."
   (let ((cj/--webclip-url "https://example.com")
         (cj/--webclip-title "Title"))
     (cl-letf (((symbol-function 'require) (lambda (&rest _) t))
-              ((symbol-function 'executable-find) (lambda (_) nil)))
+              ((symbol-function 'executable-find) (lambda (_ &rest _) nil)))
       (let ((err (should-error (cj/org-protocol-webclip-handler)
                                :type 'user-error)))
         (should (string-match-p "pandoc" (cadr err)))))))
@@ -130,7 +130,7 @@ that registers the webclip entry.  Providing `'org-protocol' fires the block."
   (let ((cj/--webclip-url "https://example.com")
         (cj/--webclip-title "Title"))
     (cl-letf (((symbol-function 'require) (lambda (&rest _) t))
-              ((symbol-function 'executable-find) (lambda (_) "/usr/bin/pandoc"))
+              ((symbol-function 'executable-find) (lambda (_ &rest _) "/usr/bin/pandoc"))
               ((symbol-function 'org-web-tools--url-as-readable-org)
                (lambda (_) "* Page Title\n** Sub heading\nBody.\n"))
               ((symbol-function 'message) #'ignore))
@@ -142,7 +142,7 @@ that registers the webclip entry.  Providing `'org-protocol' fires the block."
   (let ((cj/--webclip-url "https://example.com")
         (cj/--webclip-title "Title"))
     (cl-letf (((symbol-function 'require) (lambda (&rest _) t))
-              ((symbol-function 'executable-find) (lambda (_) "/usr/bin/pandoc"))
+              ((symbol-function 'executable-find) (lambda (_ &rest _) "/usr/bin/pandoc"))
               ((symbol-function 'org-web-tools--url-as-readable-org)
                (lambda (_) "* Page Title\n** Sub heading\nBody.\n"))
               ((symbol-function 'message) #'ignore))